1. Field of the Invention
The present invention relates to a novel photopolymerizable composition and a novel recording material. More particularly, it relates to a photopolymerizable composition and a recording material that can be suitably used in various fields including inks, color filters, holograms, proofs, sealants, adhesives, lithographic printing, resin relief printing and photoresists.
2. Description of the Related Art
A photopolymerizable composition basically contains a photopolymerization initiator and a compound having two or more ethylenic unsaturated bonds that can be addition-polymerized (hereinafter referred to as a xe2x80x9cpolyfunctional monomerxe2x80x9d). The photopolymerizable composition is hardened upon irradiation with light to change the cohesiveness thereof, and becomes insoluble in solvents. By utilizing this property, the photopolymerizable composition is widely used in photography, printing, surface treatment of metals, and inks. The functions and applications of the photopolymerizable composition have been described in various publications.
For example, details thereof have been described by J. Koser in xe2x80x9cLight Sensitive Systemsxe2x80x9d, pp. 158 to 193 (J. Wiley and Sons, New York, 1965) and by K. I. Jacobson and R. E. Jacobson in xe2x80x9cImaging Systemsxe2x80x9d, pp. 181 to 222 (J. Wiley and Sons, New York, 1976).
In recent years, an image forming system utilizing photosensitive microcapsules containing therein a photopolymerizable composition has been proposed as an image forming process utilizing a photopolymerizable composition. For example, JP-A-57-124343, JP-A-57-179836 and JP-A-57-197538 disclose such a process in which a coloring sheet coated with a photopolymerizable composition containing a vinyl compound and a photopolymerization initiator and microcapsules containing a dye is exposed and then superposed on a image receiving sheet, and then pressure is applied, so as to form a dye image.
JP-A-3-87827 and JP-A-4-211252 disclose a light and heat sensitive coloring recording material containing two components that are electron donating and electron accepting, respectively. They disclose a recording material, in which one of the two components is contained in microcapsules, and the other is a hardening compound of a photocuring composition which is a recording material. The second component may also be contained in the microcapsules as well as in the photocuring composition. In the recording material, described hereinafter, such a light and heat sensitive recording material is exemplified that has a layer containing microcapsules containing an electron donating colorless dye, and further contains, outside the microcapsules, a photocuring composition containing an electron accepting compound, a polymerizable vinyl monomer and a photopolymerization initiator.
As described in the foregoing, a recording material utilizing a photopolymerizable composition can attain image recording in a completely dry system without the use of a developing solution, and therefore it is particularly preferred in view of environmental protection because no waste is generated.
It is advantageous in the case where image recording is carried out on a photosensitive recording material that an infrared laser and blue to red light, which are inexpensive, can be utilized in addition to ultraviolet light and visible light having short wavelengths. However, a recording material utilizing a photopolymerizable composition is sensitive to ultraviolet light, but most of them are not sensitive to light in the visible to infrared region, or have insufficient sensitivity in the case where they are sensitive. As a result, an image thus formed is blurred, and the contrast between the image part and the non-image part is low. Therefore, there is a demand for the recording material utilizing a photopolymerizable composition in which the sensitivity upon image recording with light in the visible to infrared region is further increased.
These recording materials generally contain a spectral sensitizing dye for increasing the sensitivity to light used for image recording (writing). However, because a spectral sensitizing dye has a hue, it is necessary that after obtaining an image thus recorded, the recording material is irradiated with light that can be absorbed by the dye to photodecompose the dye, whereby the color present on the recording material is erased. When the decolorization is insufficient, deterioration in sharpness of hues and contrast occurs due to residual color in portions. Furthermore, such a problem arises that the decolorization requires a long period of time. Therefore, further improvement of the spectral sensitizing dye has been demanded.
The invention has been developed to solve the problems associated with the conventional art.
An object of the invention is to provide a photopolymerizable composition that is highly sensitive not only to ultraviolet light, but also to light in the range from visible light to infrared light.
Another object of the invention is to provide such a recording material for a completely dry treatment system which generates no waste and is capable of carrying out image recording with high sensitivity by using not only ultraviolet light but also light in the range from visible light to infrared light, is excellent in decolorization of the non-image part (the background part), and is capable of forming a monochrome or color image with sharpness and high contrast.
The foregoing objects of the invention will be attained by the following aspects of the invention.
The invention relates to, as a first aspect, a photopolymerizable composition comprising a polymerizable compound having an ethylenic unsaturated bond, a compound represented by the following general formula (I), and a radical generator capable of forming a radical by the action of said compound and said radical generator upon each other: 
wherein R1 and R2 each independently represents an aliphatic group or an aromatic group; Y1 and Y2 each independently represents a sulfur atom, an oxygen atom, C(R3)R4, a selenium atom or a tellurium atom, and R3 and R4 each independently represents a hydrogen atom, an aliphatic group or an aromatic group, provided that R3 and R4 are atomic groups which form a ring by bonding with each other. The aliphatic group and the aromatic group are defined in the same way as the aliphatic group and the aromatic group represented by R1 or R2 in the general formula (I); Z1 represents an atomic group forming an aromatic heterocyclic ring or an aromatic ring formed by condensation of heterocyclic rings, wherein the heterocyclic ring may have a substituent; Z2 represents an atomic group forming an aromatic ring or a heterocyclic ring, wherein the aromatic ring and the heterocyclic ring each may have a substituent; L1, L2 and L3 each independently represents a methine group which may or may not have a substituent, wherein when L1, L2 and L3 each is a methine group having a substituent, the substituents may bond to form an unsaturated aliphatic ring or an unsaturated heterocyclic ring; n represents 0, 1, 2 or 3; and Xxe2x88x92 represents a group capable of forming an anion.
The radical generator is preferably an organic boron compound, and the organic boron compound is preferably a compound represented by the following general formula (A): 
Wherein Ra1, Ra2, Ra3 and Ra4 each independently represents an aliphatic group, an aromatic group, a heterocyclic group or Si(Ra5)(Ra6)xe2x80x94Ra7, wherein Ra5, Ra6 and Ra7 each independently represents an aliphatic group or an aromatic group; and G+ represents a group capable of forming a cation.
The invention relates to, as a second aspect, a recording material comprising a support having thereon a recording layer, the recording layer at least comprising a color forming component A, a color forming component B having a site that causes the coloring component A to form color upon reacting therewith, and the photopolymerizable composition of the invention.
At least one of the polymerizable compounds having an ethylenic unsaturated bond may be the color forming component B, and the polymerizable compound having an ethylenic unsaturated bond maybe a color-formation suppressing compound having, in the same molecule, a site that suppresses the reaction between the color forming component A and the color forming component B. The color forming component A may be contained in microcapsules.
Furthermore, the recording layer may have a multi-layer structure comprising i pieces of recording layers containing from a first recording layer that is sensitive to light having a center wavelength xcex1 and a second recording layer that is sensitive to light having a center wavelength xcex2 and forms a color different from that of the first recording layer to the i-th recording layer that is sensitive to light having a center wavelength xcexi and forms a color different from those of the first to (i-l)th recording layers.